Recent studies have suggested that successful antitumor responses consisted of a combination of T cell-mediated and non-T cell-mediated mechanisms. We have used transplantable mouse renal and autochthonous mammary carcinoma models to demonstrate that the systemic administration of the combination of IL-2 + IL-12 yields enhanced antitumor effects against even well-established metastatic cancers. Specifically, the systemic administration of IL-12/pulse IL-2 induces complete regression of established renal cancer by a mechanism that is dependent on CD8+ T cells and the production of interferon-gamma (IFNg). Histologic sections from mice treated with IL-12/IL-2 reveal large bands of necrosis and a clear reduction in vascularity that is macroscopically evident via a novel latex infusion method. The IL-12/IL-2 combination potently enhances, in an IFNg- dependent manner, the expression of genes encoding the antiangiogenic chemokines IP-10 and MIG but not the genes that code for such proangiogenic mediators (i.e. VEGF, TGFbeta, angiogenin, FLT-1, or FLK-1), as well as Fas and FasL within the local tumor site. The induction of Fas and FasL in the tumor bed correspond to an increase in apoptosis in the tumor site. Further, we have also observed that IL- 12/pulse IL-2 can induce complete regression of established tumor in a transgenic model of spontaneous mammary carcinoma. Administration of IL- 12/IL-2 enhances expression of genes encoding Fas and FasL, as well as the antiangiogenic chemokines IP-10 and MIG within established tumors. Treatment of mice bearing established mammary carcinoma with IL-12/IL-2 also prevents the emergence of new tumors compared to the progressive multifocal mammary carcinomas that develop in control mice. Administration of Administration of IL-12/IL-2 to juvenile transgenic mice delays the progressive hyperplasia, atypia and overt carcinoma that emerges in control mice, and markedly enhances local T-cell infiltration, Fas/FasL gene expression and apoptosis in the mammary sites of treated mice. These results suggest that successful biological therapy may depend on a complex combination of immune-mediated and immune- dependent(i.e. antiangiogenic) events. Our present studies are focused on determining the relative contributions of these processes to antitumor responses induced by IL-12/IL-2, and the molecular mechanisms that regulate them. In addition, we are pursuing appropriate collaborative relationships to perform non-human primate toxicology of the IL-12/IL-2 combination, as a precursor to a Phase I clinical trial of this cytokine combination.